Loosely coupled (shunted) transformers have been used in the prior art in many settings and applications. For examples, to control current when power is supplied to various type of loads or in inductive wireless power transfer applications. Loosely coupled transformers have higher leakage reactance compared to standard transformers that are tightly coupled and their coupling coefficient is less than standard transformers. Loosely coupled transformers have an air gap between primary and secondary coils. Generally, an E-shaped or multi-legged magnetic core is employed with the air gapped legs. The type and geometry of the coils and cores can be different and depends on the application.
Characteristics of loosely coupled transformers can affect the performance of systems in which the loosely coupled transformers are applied. Depending on the application, these characteristics, including primary and secondary coils' self-inductances, mutual inductance between primary and secondary coils and primary and secondary coils' ESRs, have a significant influence on the system performance.
An example of loosely coupled transformers are in plug-in hybrid-electric vehicles (PHEV) and battery electric vehicles (BEV) which include a traction battery for powering the vehicle. The vehicle can be coupled to an external power source to charge the traction battery. The vehicle may support wireless charging of the traction battery. Wireless charging is accomplished by the use of coils in the charging system and the vehicle. Power is inductively transferred from the charging system to the vehicle through the coils. Alignment of the charging coils may be accomplished by a charge port in which a charge handle is inserted. Other systems may rely on the driver to align the charging coils. For example, the charging system may include a coil in the floor of a charge station. The vehicle may include a coil on an underside of the vehicle that may be in proximity to the floor coil when the vehicle is positioned in the charge station. Effectiveness of the charging may depend on the relative alignment of the coils.